The present invention relates to suspension systems and more particularly to a simplified lockout device for a suspension system that includes an adjustable “blow-off” mechanism. The present invention also relates to a simplified flow restrictive device for a suspension system that includes an adjustable pressure relief mechanism.
Suspension systems, typically used on handlebar-steered vehicles such as bicycles and motorcycles, are designed to absorb the impacts and vibrations typically experienced by riders when the bicycle traverses irregularities on the riding surface. Suspension systems may be positioned in or proximate to the front and rear forks, seat tube, head tube, and other bicycle frame locations to insulate the rider from vibrations and impacts. Suspension performance may be affected by various factors such as rider weight, rider skill and terrain conditions. One particular factor that may affect suspension performance is rider induced, namely, the pedaling force exerted by the rider on the frame of the bicycle. The pedaling action of the rider loads the suspension, resulting in up and down bobbing motion of the bicycle. On rough terrain, some bobbing motion is an acceptable side effect of a fully active suspension capable of absorbing large bumps. Generally however, on smooth terrain, this motion dissipates the rider's energy, energy that could be used to propel the bicycle forward.
To solve this problem, bicycle suspension systems have been designed with a device that allows the suspension to be turned on or off. When the suspension is on, it is active and displaces in response to bumps in the road. When the suspension is off or “locked out”, it becomes substantially rigid and does not displace in response to road irregularities. In a suspension system that is hydraulically dampened, the suspension typically includes a pair of telescopically arranged cylinders, a compression piston, a valve mechanism that defines two fluid chambers and a lockout mechanism manually operable by the rider between closed and open positions to control fluid flow between the two chambers. Generally, the suspension dampens or slows down the speed of the fork in response to an applied load as the fluid is forced across the valve mechanism through a restrictive orifice. The size of the orifice determines the amount of damping that will occur. To completely restrict the flow of the fluid, the valve mechanism may be closed to cover the orifice and the fork becomes substantially rigid or locked out.
One problem associated with prior art lockout mechanisms is that damage may occur to the system while in the lockout mode under a large jarring compression load. To prevent such damage, a blow-off mechanism may be provided to relieve the pressure on the suspension when an applied force reaches a critical level. Usually, the blow-off includes a valve mechanism separate from the lockout valve mechanism. Typically, the blow-off valve mechanism is biased toward a closed position by a preloaded spring and is opened when the fluid pressure produced by the compression of the lockout piston is high enough to overcome the force of the preloaded spring. Once the blow-off valve has “blown off,” a lightly sprung return valve allows the fluid to return to the compression chamber. The blow-off and return valves are typically both one-way valves that permit flow in only one direction. There are several problems with this configuration including the complexity and higher cost of having three different valve mechanisms, including the additional parts needed to actuate the valves, and the need to machine three valve quality surfaces.
Another problem associated with conventional blow-off mechanisms is the inability to adjust the blow-off force. For example, pedaling forces will typically be higher for a heavier rider than for a lighter rider requiring a higher blow-off setting. A blow-off force, properly set to prevent a heavier rider from blowing off the fork while pedaling, may be set too high for a lighter rider to reach blow-off under normal riding conditions. Therefore, there is a need to provide a bicycle suspension with a lockout mechanism that has fewer parts and an adjustable blow-off mechanism.